Changes in thermo-tolerance and survival under simulated gastrointestinal conditions of Salmonella Enteritidis PT4 and Salmonella Typhimurium PT4 in chicken breast meat after exposure to sequential stresses

Effects of intrinsic characteristics of Salmonella enterica strains isolated from foods and humans, and their interaction with food matrices during simulated gastric conditions

The stomach's acidic pH is a crucial barrier against foodborne pathogens such as Salmonella enterica. This study investigated the survival of S. enterica under simulated oral and gastric conditions (SGC; pH 2 for 120 min) as a function of intrinsic pathogen characteristics and food matrix. Fifty-seven S. enterica strains isolated from food and human infections (previously characterized by serotype, virulotype, multi-drug resistance, isolation source, and isolation season) were subjected to SGC using water as a vehicle. Population reduction among the 57 isolates ranged from 2.7 to 4.7 log CFU, revealing that human isolates were inactivated less than food isolates (p = 0.0008). Among food strains, strains isolated during the cold season (food sampled from December to February) displayed the highest reduction (p = 0.00002). Six representatives of the 57 S. enterica strains were selected according to their virulotype and antimicrobial profile. They were further used to evaluate their survival under SGC in four food matrices (water, mango, tomato, and chicken), measuring S. enterica at 30 min intervals. The strains in chicken showed the lowest reduction and inactivation rate (1.42 ± 0.35 log CFU; 0.03 ± 0.005 min-1), followed by tomato (3.75 ± 0.57 log CFU; 0.15 ± 0.02 min-1), water (4.23 ± 0.27 log CFU; 0.17 ± 0.02 min-1), and mango (4.49 ± 0.39 log CFU; 0.17 ± 0.03 min-1). These data suggest that not all S. enterica strains have the same ability to survive under SGC, influencing the probability of arriving into the small intestine.

Intermittent and Mild Cold Stimulation Maintains Immune Function Stability through Increasing the Levels of Intestinal Barrier Genes of Broilers

In order to improve the adaptability of broilers to low-temperature environments and their ability to resist acute cold stress (ACS), 240 one-day-old broilers were selected and randomly divided into three groups. The control treatment (CC) group was raised at the conventional feeding temperature from 1-43 days (d), the cold stimulation treatment (CS) group was kept at 3 °C below the temperature of CC at 1 d intervals for 3 and 6 h from 15 to 35 d, namely, CS3 and CS6, respectively. Then, all broilers were kept at 20 °C from 36 to 43 d. ACS was then carried out at 44 d, and the ambient temperature was dropped to 10 °C for 6 h. The study investigated the production performance, as well as levels of intestinal barrier genes (including Claudin-1, E-cadherin, Occludin, ZO-1, ZO-2 and Mucin2), secretory IgA in duodenum and jejunum, and immunoglobulins (IgA and IgG) in serum. The results showed that IMCS could increase the daily weight gain and decrease the feed conversion ratio. During IMCS, the expression levels of intestinal barrier genes were up-regulated and the content of secretory IgA was increased. When IMCS ceased for one week, the level of immunoglobulins in serum stabilized, and the expression levels of Occludin, ZO-2 and Mucin2 still maintained high levels. After ACS, broilers that received IMCS training maintained high levels of intestinal barrier genes and secretory IgA.

Effects of 405 ± 5-nm LED Illumination on Environmental Stress Tolerance of Salmonella Typhimurium in Sliced Beef

Salmonella Typhimurium is a widely distributed foodborne pathogen and is tolerant of various environmental conditions. It can cause intestinal fever, gastroenteritis and bacteremia. The aim of this research was to explore the effect of illumination with 405 nm light-emitting diodes (LEDs) on the resistance of S. Typhimurium to environmental stress. Beef slices contaminated with S. Typhimurium were illuminated by 405 nm LEDs (18.9 ± 1.4 mW/cm²) for 8 h at 4 °C; controls were incubated in darkness at 7 °C. Then, the illuminated or non-illuminated (control) cells were exposed to thermal stress (50, 55, 60 or 65 °C); oxidative stress (0.01% H₂O₂ [v/v]); acid stress (simulated gastric fluid [SGF] at pH 2 or 3); or bile salts (1%, 2%, or 3% [w/v]). S. Typhimurium treated by 405 nm LED irradiation showed decreased resistance to thermal stress, osmotic pressure, oxidation, SGF and bile salts. The transcription of eight environmental tolerance-related genes were downregulated by the illumination. Our findings suggest the potential of applying 405 nm LED-illumination technology in the control of pathogens in food processing, production and storage, and in decreasing infection and disease related to S. Typhimurium.

Differences in biofilm formation of Salmonella serovars on two surfaces under two temperature conditions

AIMS

Salmonella is extremely diverse, with >2500 serovars that are genetically and phenotypically diverse. The aim of this study was to build a collection of Salmonella isolates that are genetically diverse and to evaluate their ability to form biofilm under different conditions relevant to a processing environment.

METHODS AND RESULTS

Twenty Salmonella isolates representative of 10 serovars were subtyped using Clustered regularly interspaced short palindromic repeats (CRISPR)-typing to assess the genetic diversity between isolates of each serovar. Biofilm formation of the isolates on both plastic and stainless-steel surfaces at 25 and 15°C was assessed. At 25°C, 8/20 isolates each produced strong and moderate biofilm on plastic surface compared to stainless-steel (3/20 and 13/20 respectively). At 15°C, 5/20 produced strong biofilm on plastic surface and none on stainless-steel. Several isolates produced weak biofilm on plastic (11/20) and stainless-steel (16/20) surfaces. Serovar Schwarzengrund consistently produced strong biofilm while serovars Heidelberg and Newport produced weak biofilm.

CONCLUSION

These results suggest that Salmonellae differ in their attachment depending on the surface and temperature conditions encountered, which may influence persistence in the processing environment.

SIGNIFICANCE AND IMPACT OF STUDY

These differences in biofilm formation could provide useful information for mitigation of Salmonella in processing environments.

Salmonella enterica subsp. enterica virulence potential can be linked to higher survival within a dynamic in vitro human gastrointestinal model

Salmonella enterica subsp. enterica is one of the leading causes of human foodborne infections and several outbreaks are now associated with the consumption of fresh fruit and vegetables. This study aims at evaluating whether Salmonella virulence can be linked to an enhanced ability to survive successive digestive environments. Thirteen S. enterica strains were selected according to high and low virulence phenotypes. Lettuce inoculated separately with each S. enterica strain was used as food matrix in the TNO gastrointestinal model (TIM-1) of the human upper gastrointestinal tract. During the passage in the stomach, counts determined using PMA-qPCR were 2-5 logs higher than the cultivable counts for all strains indicating the presence of viable but non-cultivable cells. Bacterial growth was observed in the duodenum compartment after 180 min for all but one strain and growth continued into the ileal compartment. After passage through the simulated gastrointestinal tract, both virulent and avirulent S. enterica strains survived but high virulence strains had a significantly (p = 0.004) better average survival rate (1003 %-3753 %) than low virulence strains (from 25 % to 3730%). The survival rates of S. enterica strains could be linked to the presence of genes associated with acid and bile resistance and their predicted products. The presence of single nucleotide polymorphisms may also impact the function of virulence associated genes and play a role in the resulting phenotype. These data provide an understanding of the relationship between measured virulence potential and survival of S. enterica during dynamic simulated gastrointestinal transit.

Effect of 405-nm light-emitting diode on environmental tolerance of Cronobacter sakazakii in powdered infant formula

Cronobacter sakazakii is an opportunistic pathogen that can survive extreme desiccation, heat, acid, and osmotic stress. This can increase the risk of infection, resulting in severe diseases, mainly in neonates. The inactivation effect of 405 ± 5-nm light-emitting diode (LED) illumination on C. sakazakii with different initial concentrations and C. sakazakii strains isolated from powdered infant formula (PIF) and baby rice cereal (BRC) were firstly evaluated. Then, the effect of 405 ± 5-nm LED on the tolerance of diverse environmental conditions of C. sakazakii in PIF was investigated. Conditions involving desiccation [PIF, Water activity (a_w): 0.2-0.5], heat (45, 50, and 55 °C), acid (simulated gastric fluid: SGF, pH 4.75 ± 0.25), and bile salt (0.2%, bile salt solution) were used to study the effects of 405-nm LED on C. sakazakii resistance. The transcription levels of ten tolerance-associated genes and changes in bacterial cell membrane were examined to understand the response of C. sakazakii to LED illumination. The results showed that 405-nm LED effectively inactivated C. sakazakii ATCC 29544 with initial concentration from 8 to 1 log CFU/g in PIF and strains isolated from PIF and BRC. Moreover, 405-nm LED could decrease the tolerance of C. sakazakii in PIF to desiccation, heat treatment at 50 and 55 °C, SGF, and bile salt to different degrees, but the resistance to the heat treatment at 45 °C was not influenced by LED illumination. In addition, the transcription levels of the ten tolerance-associated genes measured in the LED-illuminated C. sakazakii cells were significantly downregulated compared with those in unilluminated controls. The damage on cell membrane was confirmed for LED-treated cells by LIVE/DEAD® assay. These results indicate that 405-nm LED illumination may be effective at reducing the environmental resistance of C. sakazakii in PIF. Furthermore, this study suggests the potential for applying 405-nm LED technology in the prevention and control of pathogens in food processing, production, and storage environments.

Genomic investigation of antimicrobial resistance determinants and virulence factors in Salmonella enterica serovars isolated from contaminated food and human stool samples in Brazil

This study investigated the antimicrobial resistance determinants, virulence factors and identified serovars in 37 Salmonella enterica strains isolated from human stool and contaminated foods linked to outbreaks that occurred in Brazil over 7 years using whole genome sequencing (WGS). Phylogenetic analysis of selected serovars (S. Typhimurium, S. Infantis, S. London, and S. Johannesburg) was performed. Ten distinct serovars were identified and, 51% of the tested strains (n = 19) showed disagreement with the previous conventional serotyping. The antimicrobial resistance (AMR) determinants or plasmids varied among the strains. Resistome analysis revealed the presence of resistance genes to aminoglycosides [aac (6')-laa, aph (3″)-lb, aph (6)-ld, aadA1 and aadA2], sulfonamides (sul1), trimethoprin (dfrA8), fosfomycin (fosA7) and tetracyclines (tetA, tetB, tetC), as well as point mutations in parC (T57S) and gyrA (S83F). Plasmidome showed the presence of IncHI2, IncHI2A, IncFIB (S), IncFII (S), IncI1 and p0111 plasmids. Eight Salmonella pathogenicity islands and up to 102 stress and/or virulence genes were identified in the evaluated genomes. Virulence genes of K88 fimbrial adhesin were first reported in S. enterica (S. Pomona, S. Bredeney and S. Mbandaka strains). pilW gene was first identified in S. Pomona. Phylogenetic analysis showed that some serovars circulated in Brazil for decades, primarily within the poultry production chain. Findings highlighted the virulence and AMR determinants in strains that may lead to recurring food outbreaks.

Salmonella Contamination of Broiler Chicken Carcasses at Critical Steps of the Slaughter Process and in the Environment of Two Slaughter Plants: Prevalence, Genetic Profiles, and Association with the Final Carcass Status

ABSTRACT

Salmonella is a foodborne pathogen commonly associated with poultry products. The aims of this work were to (i) estimate the impact of critical steps of the slaughter process on Salmonella detection from broiler chicken carcasses in two commercial poultry slaughter plants in Quebec, Canada; (ii) investigate the presence of Salmonella in the slaughter plant environment; (iii) describe, using a high-resolution melting (HRM) approach, the HRM Salmonella profiles and serotypes present on carcasses and in the slaughter plant environment; and (iv) evaluate whether the HRM flock status after chilling could be predicted by the flock status at previous steps of the slaughter process, the status of previous flocks, or the status of the processing environment, for the same HRM profile. Eight visits were conducted in each slaughter plant over a 6-month period. In total, 379 carcass rinsates from 79 flocks were collected at five critical steps of the slaughter process. Environmental samples were also collected from seven critical sites in each slaughter plant. The bleeding step was the most contaminated, with >92% positive carcasses. A decrease of the contamination along the slaughtering process was noted, with carcasses sampled after dry-air chilling showing ≤2.5% Salmonella prevalence. The most frequently isolated serotypes were Salmonella Heidelberg, Kentucky, and Schwarzengrund. The detection of the Salmonella Heidelberg 1-1-1 HRM profile on carcasses after chilling was significantly associated with its detection at previous steps of the slaughter process and in previously slaughtered flocks from other farms during a same sampling day. Results highlight the importance of the chilling step in the control of Salmonella on broiler chicken carcasses and the need to further describe and compare the competitive advantage of Salmonella serotypes to survive processing. The current study also illustrates the usefulness of HRM typing in investigating Salmonella contamination along the slaughter process.

HIGHLIGHTS

A dynamic and integrated in vitro/ex vivo gastrointestinal model for the evaluation of the probability and severity of infection in humans by Salmonella spp. vehiculated in different matrices

The lack of proper gastrointestinal models assessing the inter-strain virulence variability of foodborne pathogens and the effect of the vehicle (food matrix) affects the risk estimation. This research aimed to propose a dynamic and integrated in vitro/ex vivo gastrointestinal model to evaluate the probability and severity of infection of foodborne pathogens at different matrices. An everted gut sac was used to determine the adhesion and invasion of Salmonella enterica and tissue damage. S. Typhimurium ATCC 14028 was used as a representative bacterium, and two matrices (water and cheese) were used as vehicles. No differences (p > 0.05) in the probability of infection (P_inf) were found for intra-experimental repeatability. However, the P_inf of cheese-vehiculated S. Typhimurium was different compared to water- vehiculated S. Typhimurium, 7.2-fold higher. The histological analysis revealed Salmonella-induced tissue damage, compared with the control (p < 0.05). In silico proposed interactions between two major Salmonella outer membrane proteins (OmpA and Rck) and digested peptides from cheese casein showed high binding affinity and stability, suggesting a potential protective function from the food matrix. The results showed that the everted gut sac model is suitable to evaluate the inter-strain virulence variability, considering both physiological conditions and the effect of the food matrix.

In vitro antibacterial activity of honey against multidrug-resistant Shigella sonnei

BACKGROUND AND PURPOSE

The health benefits of honey as an oral therapeutic agent for the treatment of diarrhoea caused by Shigella sonnei depend on the ability of honey to withstand human gastrointestinal conditions. This study aimed to investigate whether honey could withstand and inhibit the growth of Shigella sonnei under such conditions.

MATERIALS AND METHODS

We initially evaluated the survival of Shigella sonnei in human simulated gastric conditions (SGC) and simulated intestinal conditions (SIC). This was followed by determination of the susceptibility of Shigella sonnei to Manuka and Talah honey under gastrointestinal conditions. The colony forming units (CFU) of Shigella sonnei and minimum inhibitory concentrations (MICs) of honey were calculated.

RESULTS

Shigella sonnei was unable to survive in the acidic environment of the stomach without food matrix and survived only when inoculated with a food source, resulting in 1.5 × 10⁵ ± 0.2 CFU at 60 min and 1.7 × 10⁵ ± 0.3 CFU after 120 min of incubation. In SIC, it survived both with and without food matrix at the same CFU (1.2 × 10⁷ ±0.4) at 60 min and 1.7 × 10⁷ ±0.2 CFU after 120 min of incubation. Growth of Shigella sonnei was not observed in SGC in the presence of either honey at different concentrations without a food source. In the presence of a food source, Manuka honey inhibited the growth of Shigella sonnei at 10% v/v and Talah honey at 20% v/v dilutions in SGC. In SIC, Manuka honey inhibited the growth of Shigella sonnei at 15% and 20% v/v dilutions, whereas Talah honey inhibited Shigella sonnei at 20% and 25% v/v dilutions without and with food sources, respectively.

CONCLUSION

Shigella sonnei can survive in the acidic environment of the stomach if inoculated with a food source. Acidic pH and pepsin had no deleterious effects on the antibacterial capability of honey. However, bile reduced the antibacterial activity of honey in the intestinal environment.

Successive exposure to Mentha piperita L. essential oil affects the culturability and induces membrane repair in a persister epidemic Salmonella Typhimurium PT4

This study had as aims to evaluate the effects of successive exposures to Mentha piperita L. essential oil (MPEO) on culturability and physiological functions of Salmonella Typhimurium PT4. S. Typhimurium PT4 cells (10⁸ log CFU/mL) were exposed to the same (1.25 μL/mL) or increasing MPEO concentrations (1.25-80 μL/mL) during 252 h. At each 36-h interval, the viable cell counts, and distinct cell functions were assessed using plate counting and flow cytometry, respectively. As the exposure time to the same MPEO concentration increased, the population of S. Typhimurium PT4 cells with damaged, permeabilized and depolarized membrane, and compromised efflux activity decreased. Otherwise, S. Typhimurium PT4 cells with damaged membrane physiological functions increased over the exposure to increasing concentrations of MPEO. Genomic analyses showed that the strain carries 17 genes associated with stress responses and the persistence of the tested strain among sources associated with poultry spanning more than 16 years and its virulence for humans. Therefore, successive exposure to a sublethal concentration of MPEO induced S. Typhimurium PT4 cells capable of maintaining the membrane integrity and its functions despite their non-culturable state.

Heat shock protein 70 protects the quail cecum against oxidant stress, inflammatory injury, and microbiota imbalance induced by cold stress

The intent of this study was to investigate the effects of cold stress on oxidative indexes, inflammatory factors, and microbiota in the quail cecum. A total of 192 male quails (15-day-old) were randomly divided into 12 groups (16 in each group) and were exposed to acute (up to 12 h) and chronic (up to 20 D) cold stress at 12 ± 1°C. After cold stress treatment, we examined morphological damage, oxidative stress indexes, inflammatory factors, and intestinal microbiota. Results of morphological examination showed that both acute and chronic cold stress can lead to cecal tissue injury. In addition, both acute and chronic cold stress, especially chronic cold stress can influence the activity of oxidative stress mediators. Glutathione (GSH) and glutathione peroxidase (GSH-Px) activities decreased significantly (p < 0.05), while the nitric oxide (NO) content and inducible nitric oxide synthase (iNOS) activity increased significantly (p < 0.05). Moreover, mRNA levels of inflammatory factors cyclooxygenase-2 (COX-2), prostaglandin E synthase (PTGES), and heat shock protein 70 (Hsp70) were higher in both acute and chronic cold stress groups when compared with the control group (p < 0.05). Furthermore, the intestinal microbiota was changed in both the acute and chronic cold stress groups. These results suggested that cold stress caused oxidative stress and inflammatory injury in cecal tissues, influenced cecal microbiota, and increased expression of Hsp70, which may contribute in protecting the cecum against cold stress in quails.

Expression of DnaK and HtrA genes under high temperatures and their impact on thermotolerance of a Salmonella serotype isolated from tahini product

Background

Salmonella is considered to be the second largest source of infection in food-borne diseases. It is also considered one of the most important dangers particularly in the meat and dairy industry. Therefore, the main objective of our study was to determine the relationship between thermotolerance of a Salmonella serotype and the expression of DnaK and HtrA genes.

Results

In this study, expression of the two genes DnaK and HtrA was compared under four different temperatures 37 °C, 42 °C, 50 °C, and 55 °C in two serotypes of Salmonella enterica subsp. enterica. One of them was isolated from tahini product and identified as Salmonella enterica subsp. enterica serovar choleraesuis. This identified serotype was found to be more thermotolerant than the second serotype (Salmonella enterica subsp. enterica serovar typhimurium (ATCC 13311)), which was used as reference. This conclusion was based on D and Z values, which were used to compare thermoresistance ability of the two serotypes under four different temperatures 60 °C, 65 °C, 70 °C, and 75 °C. In addition, the results of qRT-PCR showed that after 43 °C (induction temperature), the relative expression (fold change) of DnaK and HtrA genes increased up to 5 and 47, respectively, comparing to their expression at 37 °C.

Conclusions

Thermotolerance of the identified S. choleraesuis serotype showed significantly high expression levels of DnaK and HtrA genes.

Efficacy of oregano and rosemary essential oils to affect morphology and membrane functions of noncultivable sessile cells of Salmonella Enteritidis 86 in biofilms formed on stainless steel

AIMS

This study evaluated the efficacy of essential oil from Origanum vulgare L. (oregano; OVEO) and Rosmarinus officinalis L. (rosemary; ROEO) to inactivate sessile cells of Salmonella enterica serovar Enteritidis 86 (SE86) in young and mature biofilms formed on stainless steel.

METHODS AND RESULTS

Ultrastructural alterations and damage in different physiological functions caused by OVEO and ROEO in noncultivable sessile cells of SE86 were investigated using scanning electron microscopy and flow cytometry. OVEO (2·5 μl ml^-1 ) and ROEO (40 μl ml^-1 ) were effective to eradicate young and mature biofilms formed by SE86 sessile cells on stainless steel surfaces; however, the efficacy varied with exposure time. OVEO and ROEO caused alterations in morphology of SE86 sessile cells, inducing the occurrence of bubbles or spots on cell surface. OVEO and ROEO compromised membrane polarization, permeability and efflux activity in noncultivable SE86 sessile cells. These findings show that OVEO and ROEO act by a multitarget mechanism on SE86 membrane functions.

CONCLUSIONS

ROEO and OVEO showed efficacy to eradicate SE86 sessile cells in preformed biofilms on stainless steel, displaying a time-dependent effect and multitarget action mode on bacterial cell membrane.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study provides for the first time the effects of OVEO and ROEO on morphology and physiological functions of noncultivable sessile cells of S. Enteritidis biofilms preformed on stainless steel surfaces.

An ordinal logistic regression approach to predict the variability on biofilm formation stages by five Salmonella enterica strains on polypropylene and glass surfaces as affected by pH, temperature and NaCl

This study assessed the adhesion and formation of biofilm by five Salmonella enterica strains (S. Enteritidis 132, S. Infantis 176, S. Typhimurium 177, S. Heidelberg 281 and S. Corvallis 297) on polypropylene (PP) and glass (G) surfaces as affected by pH (4-7), NaCl concentration (0-10% w/v) and temperature (8-35 °C). Sessile counts <3 log CFU/cm² were considered lack of adhesion (category 1), while counts ≥ 3 and < 5 log CFU/cm² corresponded to adhesion (category 2) and counts ≥ 5 log CFU/cm² corresponded biofilm formation (category 3). The obtained results categorized in these three responses were used to develop ordinal regression models to predict the probability of biofilm stages on PP- and G-surfaces. The experimental outcomes for lack of adhesion were >90% on PP- and G-surfaces. Generally, adhesion outcomes corresponded to approximately 36% of the total, whereas biofilm outcomes were close to 65% in both PP- and G-surfaces. The biofilm stages varied among the strains studied and with the material surface under the same experimental conditions. According to the generated ordinal models, the probability of adhesion and biofilm formation on PP-surface by the five S. enterica strains tested decreased at pH 4 or 5 in NaCl concentrations >4% and at a temperature <20 °C. On G-surface, the probability of adhesion increased pH 6 or 7, in the absence of NaCl and temperatures <20 °C, while, the probability of biofilm formation increased in the same pH, NaCl concentration up to 4% and temperatures ≥20 °C. This is the first study assessing the biofilm formation through categorical, ordinal responses and it shows that ordinal regression models can be useful to predict biofilm stages of S. enterica as a function of pH, NaCl, and temperature or their interactions.

Survival and Environmental Stress Resistance of Cronobacter sakazakii Exposed to Vacuum or Air Packaging and Stored at Different Temperatures

The aim of this study was to evaluate the survival of Cronobacter sakazakii exposed to vacuum or air packaging, then stored at 4, 10, or 25°C, and the environmental stress resistance of vacuum-packaged or air-packaged bacterial cells were determined by subjecting the cells to reconstituted infant formula at 50°C, in acid (simulated gastric fluid, pH = 3.5), and in bile salt [bile salt solution, 5% (wt/vol)]. A cocktail culture of C. sakazakii desiccated on the bottom of sterile petri plates was air-packaged or vacuum-packaged and then stored at 4, 10, or 25°C for 10 days. The viable cell populations during storage were examined, and the vacuum-packaged and air-packaged cells (stored at 10°C for 4 days) were subsequently exposed to heat, acid, or bile salt. The results show that the populations of vacuum-packaged and air-packaged C. sakazakii were reduced by 1.6 and 0.9 log colony-forming units (CFU)/ml at 4°C and by 1.6 and 1.3 log CFU/ml at 25°C, respectively, in 10 days. At 10°C, significant reductions of 3.1 and 2.4 log CFU/ml were observed for vacuum-packaged and air-packaged cells, respectively. Vacuum packaging followed by storage at 10°C for 4 days caused significant decreases in the resistance of C. sakazakii to heat, acid, and bile salt conditions compared with air packaging. These results suggest that the application of vacuum packaging for powdered infant formula could be useful to minimize the risk of C. sakazakii.

Quantitative assessment of tolerance response to stress after exposure to oregano and rosemary essential oils, carvacrol and 1,8-cineole in Salmonella Enteritidis 86 and its isogenic deletion mutants ∆dps, ∆rpoS and ∆ompR

This study assessed the influence of rpoS, dps and ompR genes on the tolerance response of Salmonella Enteritidis 86 (SE86) to homologous and heterologous stressing agents after exposure to essential oils (EOs) from Origanum vulgare L. (oregano; OVEO) and Rosmarinus officinalis L. (rosemary; ROEO) and their major constituents (ICs), carvacrol (CAR) and 1,8-cineole (CIN), respectively, by modelling the log reduction over time. Minimum inhibitory concentration values of OVEO (1.25 μL/mL), CAR (0.62 μL/mL), ROEO (20 μL/mL) and CIN (10 μL/mL) against SE86 were always one-fold higher than those against ∆dps, ∆rpoS and ∆ompR mutants. Exposure to the same concentration of OVEO, CAR, ROEO or CIN caused higher reductions (up to 2.5 log CFU/mL) in ∆dps, ∆rpoS and ∆ompR mutants than in SE86 in chicken broth. In assays with homologous stressing agents, ompR, dps and rpoS influenced the tolerance to OEs or ICs. After adaptation to OVEO, CAR, ROEO and CIN, osmotolerance and acid tolerance of SE86 were influenced by rpoS gene, while thermotolerance of SE86 was influenced by ompR. Tolerance of SE86 to sodium hypochlorite after adaptation to OEs or ICs was influenced by rpoS and dps. These findings quantitatively describe for the first time the influence of rpoS, dps and ompR genes on the tolerance of Salmonella Enteritidis to OVEO, CAR, ROEO and CIN.

Changes of Antibiotic Resistance Phenotype in Outbreak-Linked Salmonella enterica Strains after Exposure to Human Simulated Gastrointestinal Conditions in Chicken Meat

Fifteen outbreak-linked Salmonella enterica strains in chicken meat were evaluated under simulated human gastrointestinal conditions for their resistance and susceptibility to 11 antibiotics from seven antibiotic classes. The MIC of each antibiotic was determined by microdilution in broth before and after the exposure of each strain to a continuous system simulating the conditions in the human mouth, esophagus-stomach, duodenum, and ileum. Strains were inoculated onto chicken breast (9 g; inoculated at 5 log CFU/g) prior to exposure. Data were interpreted according Clinical and Laboratory Standards Institute breakpoints. After the in vitro digestion, 12 Salmonella strains with reduced susceptibility to ciprofloxacin (CIP) changed to CIP resistant. The ceftriaxone (CTX)-intermediate Salmonella Newport strain changed to CTX resistant. The ampicillin (AMP)-susceptible Salmonella Heidelberg strain changed to AMP resistant, and the sulfamethoxazole-trimethoprim (SXT)-susceptible strains of Salmonella serovars Typhimurium, Agona, Newport, Albany, and Corvallis changed to SXT resistant. The Salmonella Heidelberg, Salmonella Newport, Salmonella Albany, and Salmonella Corvallis strains had the highest frequency of changes in antibiotic susceptibility with new resistant phenotypes to AMP and CIP, CTX and SXT, CIP and SXT, and CIP and SXT, respectively. Conditions imposed by a simulated gastrointestinal environment changed the susceptibility of S. enterica strains to clinically relevant antibiotics and should be considered in the selection of therapies for human salmonellosis.

Predicting adhesion and biofilm formation boundaries on stainless steel surfaces by five Salmonella enterica strains belonging to different serovars as a function of pH, temperature and NaCl concentration

This study aimed to assess the capability of 97 epidemic S. enterica strains belonging to 18 serovars to form biofilm. Five strains characterized as strong biofilm-producers, belonging to distinct serovars (S. Enteritidis 132, S. Infantis 176, S. Typhimurium 177, S. Heidelberg 281 and S. Corvallis 297) were assayed for adhesion/biofilm formation on stainless steel surfaces. The experiments were conducted in different combinations of NaCl (0, 2, 4, 5, 6, 8 and 10% w/v), pH (4, 5, 6 and 7) and temperatures (8 °C, 12 °C, 20 °C and 35 °C). Only adhesion was assumed to occur when S. enterica counts were ≥3 and <5 log CFU/cm², whereas biofilm formation was defined as when the counts were ≥5 log CFU/cm². The binary responses were used to develop models to predict the probability of adhesion/biofilm formation on stainless steel surfaces by five strains belonging to different S. enterica serovars. A total of 99% (96/97) of the tested S. enterica strains were characterized as biofilm-producers in the microtiter plate assays. The ability to form biofilm varied (P < 0.05) within and among the different serovars. Among the biofilm-producers, 21% (20/96), 45% (43/96), and 35% (34/96) were weak, moderate and strong biofilm-producers, respectively. The capability for adhesion/biofilm formation on stainless steel surfaces under the experimental conditions studied varied among the strains studied, and distinct secondary models were obtained to describe the behavior of the five S. enterica tested. All strains showed adhesion at pH 4 up to 4% of NaCl and at 20 °C and 35 °C. The probability of adhesion decreased when NaCl concentrations were >8% and at 8 °C, as well as in pH values ≤ 5 and NaCl concentrations > 6%, for all tested strains. At pH 7 and 6, biofilm formation for S. Enteritidis, S. Infantis, S. Typhimurium, S. Heidelberg was observed up to 6% of NaCl at 35 °C and 20 °C. The predicted boundaries for adhesion were pH values < 5 and NaCl ≥ 4% and at temperatures <20 °C. For biofilm formation, the predicted boundaries were pH values < 5 and NaCl concentrations ≥ 2% and at temperatures <20 °C for all strains. The secondary models obtained describe the variability in boundaries of adhesion and biofilm formation on stainless steel by five strains belonging to different S. enterica serovars. The boundary models can be used to predict adhesion and biofilm formation ability on stainless steel by S. enterica as affected by pH, NaCl and temperature.

Lipids, pH, and Their Interaction Affect the Inhibitory Effects of Carvacrol against Salmonella Typhimurium PT4 and Escherichia coli O157:H7

Although carvacrol (CAR) is considered an alternative antimicrobial for use in food, few is known about the influence of food-related parameters on its inhibitory effects against pathogens. This study assessed the influence of different amounts of proteins, using beef extract (BE) as a protein-rich source, lipids (LIP), using sunflower oil as a LIP-rich source, and pH values or their interaction on the inhibitory effects of CAR against Salmonella Typhimurium PT4 (ST) and Escherichia coli O157:H7 (EC). The specific maximum growth rate (μmax) and lag phase duration (λ) of the test pathogens when exposed to CAR in media with different amounts of BE (4, 6, and 8 g/100 mL), LIP (3.75, 5, and 6.25 mL/100 mL), and pH values (5, 5.5, and 6) were determined. The viable counts of the tested pathogens in media that promoted the highest and lowest μmax in the presence of CAR were monitored during 24 h. The lowest μmax of ST and EC exposed to 2.4 μL/mL (-1.29 and -0.82 log CFU/mL/h, respectively) or 4.8 μL/mL CAR (-1.44 and -2.17 log CFU/mL/h, respectively) were observed in media with the highest LIP amount (6.25 mL/100 mL) and pH value (pH 6). For both SE and EC, the longest λ (> 2 h) was verified in media where these pathogens showed the lowest μmax. These data indicate that the concomitant increase in LIP amounts and pH values affected positively the CAR inhibitory effects against the target pathogens. CAR (2.4 or 4.8 μL/mL) failed to inhibit the increase in ST and EC counts in media where the highest μmax values were previously observed. On the contrary, CAR inhibited the increase of ST counts (final counts 5 log CFU/mL) and decreased the EC counts (final counts 3.5 log CFU/mL) in media where the lowest μmax values were observed. These results show that the inhibitory effects of CAR on ST and EC in food matrices could be affected as a function of the interaction of LIP amounts and pH values.